1. Field of the Invention
The present invention relates generally to optical fiber, and particularly optical fibers which have large effective area and low bend loss at 1550 nm.
2. Technical Background
Optical amplifier technology and wavelength division multiplexing techniques are typically required in telecommunication systems that provide high power transmissions for long distances. The definition of high power and long distances is meaningful only in the context of a particular telecommunication system wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. There are additional factors, known to those skilled in the art, which have impacted upon the definition of high power and long distance. However, for most purposes, high power is an optical power greater than about 10 mW. In some applications, single power levels of 1 mW or less are still sensitive to non-linear effects, so that the effective area is still an important consideration in such lower power systems.
Generally, an optical waveguide fiber having a large effective area (Aeff) reduces non-linear optical effects, including self-phase modulation, four-wave-mixing, cross-phase modulation, and non-linear scattering processes, all of which can cause degradation of signals in high powered systems.
On the other hand, an increase in effective area of an optical waveguide fiber typically results in an increase in macrobending induced losses which attenuate signal transmission through a fiber. The macrobending losses become increasingly significant over long (e.g., 100 km, or more) distances (or spacing between regenerators, amplifiers, transmitters and/or receivers. Unfortunately, the larger the effective area of a conventional optical fiber is, the higher the macrobend induced losses tend to be.
Communication systems which typically require one gigabyte per second, and higher, transmission rates, together with regenerators spacing in excess of 100 km, typically make use of optical amplifier technology and/or wavelength division multiplexing techniques. Thus, waveguide fiber manufacturers have designed waveguides which are less susceptible to non-linear effects induced by higher power signals or by four wave mixing, which can occur in multiplexing systems.